(Koen Sebregts points out that the title of my post is misleading, since the authors explicitly state they do not predict humidity to cause complex tones. I’ll leave it unchanged as a warning to myself.)
There is a new ‘geophonetics’ paper out at PNAS this morning Climate, vocal folds, and tonal languages: Connecting the physiological and geographic dots by Caleb Everett, Damián Blasi, and Seán Roberts. In a nutshell, the claim, as I understand it, is that since low humidity is inimical to precise manipulation of vocal folds, languages with ‘complex tone’ (understood as having a more than two-way pitch-based contrast) are unlikely to thrive in regions with low humidity (i.e. hot and arid, and all types of cold). This hypothesis appears to explain the areal patterns in the prevalence of tone.
The phonetic component of the argument seems quite sound to me, and I’m not really qualified to judge the evolutionary part of this paper in any reasonable way. As a phonologist, there’s something that really bothers me though, and that is the almost total lack of critical discussion of what it means to be a tonal language. It’s noticeable that the phonological part of the bibliography is really sparse, especially compared to the phonetic part: there’s Moira Yip’s Tone textbook, several large-scale overviews like Maddieson (1978) and Hyman (2001), a couple of tonogenesis citations, and Jonathan Kaye’s (1990) textbook cited as an example of the consensus as disputed by the authors. No other work by Larry Hyman, who has published a lot on the typology of ‘tone languages’, no discussion of the whole idea of ‘pitch accent’ and how it relates to tone: the only definition given (p. 2) is ‘phonemic tone, in which pitch is used to contrast lexical meaning’. The data sources are WALS and especially the ANU phonotactics database. Both of these sources, while extremely valuable, put a lot of emphasis on documenting ‘diversity’ and quite a bit less on pinpointing what exactly it is they’re talking about.
I’ve gone to the ANU database to have a look at what it says about tone in languages I know about. Now I work on fairly ‘boring’, European languages, but recently I’ve been getting quite interested in the European ‘pitch accent’ systems, plus I actually know a bit about these languages, so I thought I’d have a go at a selection. I have to say I wasn’t exactly happy with the results. The following list gives the number of tonal contrasts given for that language in the ANU database, and my comments if any.
None of this is to say that the ANU database is bad and unusable, or that the paper is incorrect rubbish. This is a random, small selection of unrelated languages in a particular region. There is also much to be said for treating European tonal accents as a typologically unusual special case – Jakobson did that with Baltic tonal Sprachbund in 1931 already.
On the other hand, the authors are clear that their predictions should be particularly salient in relatively extreme environmental conditions, so it’s not entirely beside the point to look at northern Europe more closely. And it’s interesting that in the survey above the ANU database is consistently underreporting the number of tonal contrasts in this fairly cold, fairly dry region.
This does worry me. I’m sure the statistical models give the correct results for the data that’s fed into them. I’m willing to accept that the large amount of data might drown out this sort of noise. And yet, still, I’m finding it difficult to be convinced in matters I know little about when the things that I do know something about are a bit dodgy.
Again, this isn’t about bashing the munging of large-scale data. This paper is certainly quite explicit in its hypotheses and proposes a causal explanation based on more than correlations alone. But the data appears to have been collected without much regard to the theoretical underpinnings of what it is that we’re actually collecting here. And that means I’m not sure.